In the DNA prime, MVA boost model to be used in Project One of this application, the only immune correlate of protection against mucosal challenge identified thus far is the GM-CSF mediated avidity of vaccine-elicited antibody binding to the envelope ofthe challenge virus. The mechanism for protection is unknown but suggests an important role for the humoral immune response. The goals of the Virology and Antibody Assay Core are therefore to investigate (i) a mechanism for GM-CSF-based antibody protection (Project One), (ii) novel strategies for promoting humoral immunity within the gut mucosa (Project Two), and (iii) vaccine and challenge induced antibody specificities (NHP Monoclonal Antibody Core). The Virology Core is central to these studies and will assess whether neutralizing and Fc-mediated antibody activities correlate with vaccine-induced protection. We will focus on antibodies within mucosal secretions and plasma against viral proteins Env and Gag. The neutralizing antibody component mediates antiviral activity by binding to the virion associated form of Env and preventing infection of a target cell. While neutralizing antibodies are likely to be a critical component of a vaccine, to date no one has elicited Nabs that can mediate neutralization of genetically diverse viruses, a feature that is critical for protection of HlV-1 infected humans. Other nonneutralizing antibody activities have been associated with protection against acquisition and disease progression. These involve recognition ofthe Env expressed on the surface of an infected cell, leading to lysis of that cell (ADCC) in addition to augmenting other non-lytic mechanisms that may contribute to viral suppression (ADCVI). Finally, transmission of HIV-1 and SIV across the genital mucosa is associated with a genetic bottleneck, and we will therefore characterize the variants that establish infection in the vaccinated and control monkeys to determine whether vaccine-induced antibodies imposed selective pressure on Env. Specifically, the Virology Core will determine whether peripheral and mucosal IgG and IgA-mediated antibody activities correlate with immune protection against intravaginal challenge following vaccination and investigate whether a sieve effect is evident.